2-N-(Benzyloxycarbonyl)-L-2,4-diaminobutyric acid (I) is esterified by means of SOCl2 in MeOH to afford the corresponding methyl ester (II). Subsequent coupling of (II) with N-Boc-N-methyl-L-leucine (III) leads to dipeptide (IV). The N-benzyloxycarbonyl group of (IV) is removed by catalytic hydrogenation over Pd/C to furnish amine (V), which is further acylated with N-benzyloxycarbonyl-L-proline succinimidyl ester (VI) yielding tripeptide (VII). Then, acidic cleavage of the N-Boc protecting group (VII) produces (VIII).

Coupling of p-aminophenylacetic acid (IX) with o-tolyl isocyanate (X) produces urea (XI). This is subsequently condensed with the intermediate tripeptide (VIII) in the presence of HATU to yield amide (XII). Hydrogenolysis of the N-benzyloxycarbonyl group of (XII) then gives amine (XIII). Finally, acylation of amine (XIII) with 3,5-dichlorobenzensulfonyl chloride (XIV), followed by alkaline hydrolysis of the methyl ester group furnishes the title compound.